1. Field of the Invention
The present invention relates generally to lights, and more particularly to warning lights providing a wide-angle radiation pattern. More particularly, the present invention is directed to a warning light having a radiation pattern balanced between forward illumination and off-angle radiation in a horizontal plane.
2. Description of the Related Art
Lights serving warning function preferably provide a wide-angle light radiation pattern where the light is radiated generally parallel to the road surface. A warning pattern is distinguishable from an illumination pattern in which a wide area radiation pattern of light is directed generally toward the road surface (or other area to be illuminated) for the purpose of area illumination. U.S. Pat. No. 5,040,103, assigned to the assignee of the present invention, discloses a light assembly for wide area illumination in which a lens insert equipped with a Fresnel lens and parallel optical spreader bars cooperates with a lens cover including optical spreader bars perpendicular to those of the lens insert. The lens cover and insert spread light and direct the light generally downwardly for the purpose of area illumination.
U.S. Pat. No. 4,954,938 and 5,045,982, both assigned to the assignee of the present invention, disclose warning lights with wide-angle radiation patterns. Complex reflectors in combination with light spreading lenses provide a wide-angle radiation pattern from a compact arrangement. U.S. Pat. No. 4,866,329, also assigned to the assignee of the present invention, discloses a warning light having a wide-angle radiation pattern. This warning light is an example of a flush mounted light having an elongated paraboloidal reflector and a single light source. The wide-angle radiation pattern is provided by a convex lens secured to the reflector. The inside surface of the lens includes a plurality of parallel optical spreader bars. The spreader bars comprise generally vertically oriented elongated arcuate projections in the form of spherical surfaces separated from each other by flat areas of lens material. Light incident on the inside surface of the lens is refracted by the spreader bars to form a wide-angle radiation pattern. The spreader bars are separated by flat areas that permit some light to pass more directly through the lens to provide forward illumination.
All of these prior art designs present a compromise between lights having a simple configuration producing a simple light pattern and comparatively complex lights having widely dispersed light patterns. Typical prior art wide-angle warning lights use complicated reflector and lens configurations that result in light losses and reduced straight on visibility. Also typically, the more dispersed the light is, the less intense a warning light appears from any given position. Many of the prior art lights include a window portion directly opposite the light source to permit at least some of the light to pass through the lens or lenses unimpeded, thus improving the straight on visibility of the warning light. Naturally, it is highly desirable to provide a warning light which is capable of providing the required pattern of illumination while being of simple construction, economic to manufacture, easy to install, and not causing an increase in overall vehicle height, width, or a substantial increase in wind resistance.
It is an object of the present invention to provide a warning light which produces a wide-angle light pattern, particularly in a single preferably horizontal plane.
Another object of the present invention is to provide a warning light which is compact, i.e., is characterized by reduced height and depth, while providing light radiation of high intensity over a wide-angle.
It is a further object of the present invention to provide a light which is characterized by an efficient construction, ease of assembly and installation, and which is inexpensive to manufacture.
A still further object of the present invention is to provide a warning light in which intense light radiation is distributed in a horizontal plane through an arc of 90xc2x0 balanced to extend from an angle of 45xc2x0 offset from either side of the warning light.
Briefly stated, a preferred form of the present invention comprises a convex lens for a warning light having an inner surface including a plurality of vertically disposed prismatic elements arranged to spread light passing through the lens over an arc of 90xc2x0 in a horizontal plane. Each prismatic element comprises a rounded prism-shaped rib having parallel concave surfaces where each rib joins the inner lens surface and a convex surface connecting the two substantially planar sides of the prism. The prismatic elements are separated by quasi-flat portions of the lens having a generally uniform thickness with a large radius of curvature and which are termed flat portions. The flat portions permit light to pass through the lens in a more direct path. The refractive material and curved surfaces of the lens will result in some refraction of light incident on the flat portions, however, the angular deflection of the light and associated attenuation are minimal when compared with that of the prismatic elements.
Each prismatic element acts as a prism, with light bending upon incidence with each of the planar surfaces and bending again upon exiting the outer surface of the lens. Because the lens is preferably used in conjunction with a parabolic reflector, a significant percentage of the light incident upon each optic will have a known angle of incidence, i.e., parallel to an optical axis of the reflector. Since the reflector may not be symmetrically disposed around a center point, the term xe2x80x9coptical axisxe2x80x9d is used to identify a line perpendicular to the reflector and passing through a center point of the reflector and lens.
The invention optimizes the configuration and orientation of each prismatic element so that light parallel to the optical axis and incident on the planar surfaces of each prismatic element exits the outer surface of the lens at an angle of 45xc2x0 relative to the optical axis. Optimization of each prismatic element is accomplished by adjusting the angular orientation and configuration to compensate for the curvature of the lens. This results in light incident upon each prismatic element being consistently refracted to the desired angle without regard to the relative position of the prismatic element on the curve of the lens. The prismatic elements are generally equally spaced as they progress away from the center of the lens.
An arrangement of parallel, spaced apart prismatic elements defines a prismatic matrix that distributes light incident on the lens inner surface in a pattern having excellent straight-on visibility and additional points of brightness horizontally offset 45xc2x0 to each side of the light. The convex and concave surfaces associated with each prismatic element spread light within the 90xc2x0 arc to fill in the radiation pattern produced by the lens. The resulting wide-angle radiation pattern is produced without use of complex lenses, multiple lenses, complicated reflectors or multiple light emitting elements.
These and other objects, features and advantages of the invention will become readily apparent to those skilled in the art upon reading the description of the preferred embodiments in conjunction with accompanying drawings.